An operating lamp or a medical lamp can be dimmed to prevent the operating surgeon from being blinded due to reflection of the light by different materials. For example, light skin and white fatty tissue produce high reflection, while red tissue absorbs a relatively higher percentage of light and therefore appears darker. Dimming of the incident light from the operating lamp can also compensate for eyestrain of the operating surgeon. For example, an operation can begin with dimmed light, and the light intensity can be increased during the course of the operation to compensate for the surgeon's tiring eyes that become increasingly less sensitive.
The operating surgeon requires a lamp having light-technological properties that are independent of the brightness of the light and that are as constant as possible to ensure natural vision and optimum assessment of the illuminated objects.
Halogen lamps, gas discharge lamps, and light emitting diodes (“LEDs”) can be used as illumination sources for a medical lamp. All these illumination sources, however, have the property that the color temperature of the light considerably changes through electric and/or electronic dimming of the illumination source.
The human eye is accustomed to daylight, and human vision is adjusted to daylight, and the operating surgeon benefits from intense light that is similar to daylight. The human eye optimally recognizes contours and is able to distinguish colors and recognize movements at daylight.
For this reason, it is desirable to generate illumination conditions in an operating room that are comparable to those of daylight. Also, the area of operation does not reflect all light directed toward it but absorbs a portion of the light, and the absorption can be wavelength-dependent.
The sensory impression of color is determined by the spectral distribution of light perceived by a person, and the spectral distribution can be associated with a “color temperature” because a blackbody radiation source produces light having a spectral distribution that depends on the temperature of the radiation source. For example, daylight has a color temperature of 5,600 Kelvin. It is known from literature that, in accordance with the Kruithoff comfort curve, the color temperature of a light source should be matched with the illuminance to provide comfortable illumination conditions for humans. White light having a color temperature of approximately 4,500 Kelvin with high illuminance (>100,000 Lux) is recommended as light in operating rooms.
The ideal color temperature can be obtained by filtering light from a light source through color conversion filters. Instead of using color conversion filters, it is also possible to add colored light to white light from a source to correct the color temperature of the source.